The Cosine rule
Back to : Algebra | Sequence and Series
To solve a triangle is to find the lengths of each of its sides and all its angles.
The law of cosines is useful for computing the third side of a triangle when two sides and their enclosed angle are known, and in computing the angles of a triangle if all three sides are known.
The cosine rule is used when we are given either
[a] three sides or
[b] two sides and the included angle.
By changing which sides of the triangle play the roles of a, b, and c in the original formula, the following two formulas also state the law of cosines:
Skill builder questions
|Practice worksheet – 1||Cosine rule worksheet – 1|
|Practice worksheet – 2||Cosine rule worksheet – 2|
|Practice worksheet – 3||Cosine rule worksheet – 3|